Question

[Tran Thi Yen Nhi]

Cho tam giac ABC can o A. Ke cac duong cao BD va CE. Tren tia doi cua tia BA lay diem M, tren tia doi cua tia CA lay diem N sao cho BM=CN

a, Chung minh tam giac BEC=tam giac CDB, chung minh tam giac ECN=tam giac DBM

c,chung minh ED song song voi MN